Surround Sound Formats - Dolby Digital vs DTS vs THX

The various surround sound formats available on modern AV receivers can appear confusing.

Dolby Digital, DTS and THX listening modes are all available to
process your audio, but what is the difference and what do they all do?

On this page I list some of the audio decoding and processing
formats you will find on your hardware, and give a few details as to
when you might use them.

You may come across other audio formats in addition to those listed
here, but these are the most common and well-used. You will find that
some of the processing modes on your AV receiver are only available for
certain types of input - i.e. for analog/PCM stereo inputs or for Dolby
Digital/DTS multichannel inputs.

Dolby Digital

This will be selected automatically by an AV receiver which decodes
this format - and most receivers will support this. The most common type
of Dolby Digital is 5.1 surround sound, but there are some Dolby
Digital 2.0 soundtracks for systems with stereo speakers rather than
surround sound setups.

Dolby Digital can be sent over HDMI or optical/coaxial connections,
and the AV receiver will then decode the signal and play it as 5.1
surround sound (or stereo for DD 2.0). 'Dolby Digital' will be displayed
on the front panel display confirming it is receiving and decoding the
data stream.

This is the most common 5.1 surround sound format. It is found on
most DVDs and Blu-ray discs, and will be supported by almost all AV
receivers.

It is a lossy format, which means the original audio from the
film studio is compressed in order to fit the data on a disc. This
compression will lose some of the original sound quality, although it
still sounds pretty good on a decent sound system.

Dolby Digital EX

Some Dolby Digital soundtracks are encoded as 5.1 with an extra channel
added as part of the surround channels. This allows for an extra
surround channel at the rear - thus creating a 6.1 system.

A Dolby
Digital EX enabled receiver can decode this type of codec and
accommodate an extra surround speaker for a 6.1 setup. If there is no
extra surround speaker attached to the receiver, then it will
automatically play the 5.1 version.

Dolby Digital Plus

This codec is optional for Blu-ray and extends Dolby Digital to 7.1
surround sound. Therefore, this option may be present on a receiver that
supports 8 surround channels.

However, with the lack of 7.1
soundtracks, most studios will provide a DD 5.1 soundtrack on a disc
rather than Dolby Digital+.

Dolby TrueHD

This type of audio will be detected automatically by an AV receiver
if it has an onboard decoder. If decoded by the AV receiver, this codec
can be sent over HDMI 1.3 as a bitstream from the Blu-ray player, and
the front panel will display 'Dolby TrueHD'.

However, the ability of AV
receivers to decode this format isn't universal.

If the receiver cannot decode Dolby TrueHD, it can still play this
audio type if the Blu-ray player decodes Dolby TrueHD first, and then
sends it as LPCM.

In this instance, the front panel will display
'Multichannel Audio' (or words to that effect) - but you will still be
hearing the proper HD audio.

The advantage of Dolby TrueHD over standard Dolby Digital is it uses
lossless compression to transfer it to a disc. So, although it is still
compressed, there is no loss of audio quality from the original studio
master tapes.

On a good sound system, this will result is crisper high frequencies, deeper bass and a more-defined surround effect.

TrueHD soundtracks are only available on Blu-ray discs - they are too large for DVD discs.

Dolby Pro Logic II

Unlike the previous four codecs which are encoded on to the disc,
this is a processing format that takes a stereo audio signal and
creates a virtual 5.1 surround sound effect.

Therefore it allows those
with a 5.1 speaker setup to enjoy surround sound from sources that only
provide a stereo signal - such as most TV channels.

It also works on a
Dolby Surround 4-channel signal. It's not as good as a true 5.1
soundtrack, but it can be quite effective.

There will often be three different versions of Dolby Pro Logic II -
Movie, Music and Game. These different types have all been optimised to
suit differences in the source audio.

The 'Movie' version is designed
for stereo and Dolby Surround movies and TV shows.

The 'Music' version
allows the user to adjust the sound stage width for music sources, and
the 'Game' version is optimised for video games.

Choose the relevant
type depending on what you are listening to.

Dolby Pro Logic IIx

This is an enhancement of Dolby Pro Logic II. It converts a stereo or
5.1 soundtrack into 6.1 or 7.1 - depending on the speaker setup you have
in your room.

This will only be available on receivers that support
speaker setups greater than 5.1 and it also comes with Movie, Music and
Game versions.

Dolby Pro Logic IIz

An improvement on Dolby Pro Logic IIx. This version adds a new dimension
to surround sound - height.

The idea of Dolby Pro Logic IIz is to add
two speakers above the usual front left and right speakers to create an
even more realistic feel to certain sound effects - especially things
like wind and rain.

These height speakers can be added to a 5.1 system
to create 7.1 (with front height speakers instead of back left and
right) - or to a 7.1 system to create a 9.1 system.

Obviously the AV
receiver will need to support these speaker configurations for this to
be available.

Dolby Atmos

This is a relatively new codec
developed by Dolby, initially for use in the cinema.

However, starting in 2014,
some Blu-ray disc releases started to appear with a Dolby Atmos soundtrack. They are now more common on new releases, although not universal.

Dolby Atmos is the
first codec released that was object-based - which means that a sound object can be
placed in a more precise position in the sound-field and is not tied to a particular channel.

The simplest Dolby
Atmos speaker setup requires an extra pair of front speakers that are raised
much higher than those in a traditional 5.1 system. This allows the listener to
experience sound that moves up and down - as well as left to right.

This speaker setup, with two extra height speakers, is known as a 5.1.2 system. The height speakers are denoted by the extra .2 on the end.

This is an optional
format, and you will currently only be able to play the Dolby Atmos
soundtrack on your
disc if your AV receiver supports it. Any Blu-ray player with a minimum
HDMI 1.4 specification will be able to bitstream this to the receiver.

Basically, Dolby Atmos is layered on top of a Dolby TrueHD soundtrack. So, as long as your hardware supports TrueHD then you should be fine.

Remember, your AV receiver will need to support height speakers to play this format.

Most AV receiver manufacturers are now
releasing some models in their range that support the decoding of Dolby Atmos. In fact, even the cheaper AV receivers under $500 will often have this capability built-in.

Dolby Surround

So, Dolby Atmos sounds great, doesn't it?

However, there aren't that many Dolby Atmos soundtracks available on the discs we buy. So, what happens to our lovely height/elevation speakers when we play a standard 5.1 or 7.1 mix?

This is where Dolby Surround comes in.

Dolby Surround is an upmixing algorithm. It will take a standard surround mix and create the extra channels that your system supports.

So, if you have two (or more) height speakers installed on your AV receiver, then Dolby Surround will create channels for them from a 5.1/7.1 soundtrack.

In fact, it can also do this from a simple stereo track too.

It will work on surround systems with extra height, ceiling or upfiring speakers.

If you think this sounds very like Dolby Pro Logic IIx/z discussed above - then you would be right.

Dolby Surround is just the more modern version and is much more advanced. It can recreate placement of individual sound effects as well as height information.

This is the version you will likely find on a new AV receiver.

Not all AV receivers will come with this mode. So, check the specifications if you want this before you buy.

Also, depending on the model of receiver that you have, you may find that Dolby Surround is limited to certain types of soundtrack.

DTS

This format will be detected and decoded automatically by an AV
receiver with a DTS decoder.

Therefore, if you play a DTS soundtrack on a
Blu-ray or DVD, the receiver will accept the signal over HDMI or
coaxial/optical connections, display 'DTS' or 'DTS 5.1' on the display,
and send the audio to the 5.1 speaker system.

Like Dolby Digital, this is a lossy format, so the compression onto
disc will lose some of the original sound quality from the studio
master. However, DTS is transferred at a higher bit rate than DD, and
because of this many people say the sound of DTS is slightly better than
the Dolby version. However, the average home user will probably not
notice the difference.

DTS Neo:6

This format takes a stereo sound source and creates virtual surround
sound - either 5.1 or 6.1 depending on your hardware setup. In this
respect it does a similar thing to Dolby Pro Logic II and IIx. However,
there are differences in the resulting sound between the two systems and
so it is advisable to try both and see if you prefer one over the
other.

DTS Neo:6 comes in two versions - Cinema and Music. These are
optimised for different types of audio - movies/TV shows and music.
Switch the mode depending on the type of audio you are listening to.

It can also create a 6.1 surround mix (with the additional center surround speaker) from a 5.1 soundtrack.

DTS-ES

This will be available on some AV receivers for decoding DTS-ES
soundtracks. These versions are an extension of DTS 5.1 with an extra
surround channel encoded in the standard left and right surround
channels. The extra channel will only play on an AV receiver that has
the extra speaker installed to create a 6.1 system.

DTS-HD Master Audio

An AV receiver that can decode this type of audio on-board will
automatically switch to this setting when it detects the incoming signal
over HDMI. It will then play the multichannel audio according to the
encoded data on the disc and display 'DTS-HS Master Audio' on the front
panel display.

As already mentioned with Dolby TrueHD, there are some AV receivers
that cannot decode this type of HD audio. In this case, you will need a
Blu-ray player that can decode DTS-HD Master Audio on-board.

You can then
set the Blu-ray player to send the decoded audio to the AV receiver. This can be as LPCM over HDMI, or via its own multichannel analog outputs. If you send the decoded LPCM, the front
panel display will read 'Multichannel Audio' as it is receiving LPCM
rather than the original Master Audio data stream.

Like Dolby TrueHD, DTS-HD Master Audio uses lossless compression.
Therefore, it will sound as sharp and clear as the original studio
soundtrack.

As they are both lossless audio, there shouldn't be any difference in
audio quality between DTS-HD Master Audio and Dolby True-HD. Also, they
are only available on Blu-ray discs as the data is too large to fit on a
DVD.

DTS:X

A new innovation in surround sound audio is object-based audio soundtracks.

Started by Dolby Atmos, DTS:X is the object-based equivalent from DTS Audio, and it allows the listener to experience the audio in a more 3D fashion - with height information as well as left/right and front/back.

Your AV receiver must support the decoding of DTS:X in order for you
to enjoy this new type of audio experience.

The main difference from
Dolby Atmos is that you can experience DTS:X using a conventional 5.1 or
7.1 speaker system. You don't need to add extra hight speakers as with
Dolby Atmos.

Having said that, a DTS:X AV receiver that will support extra speaker channels will get you a greater 3D experience
if you have more speakers - especially height speakers.

As with Dolby Atmos, the bitstreaming of a DTS:X soundtrack is supported by any Blu-ray player with a minimum of HDMI 1.4 specification, so older players are supported.

DTS:X is layered on top of a DTS-HD Master Audio soundtrack, and most modern players and receivers will support this.

The important thing is that your AV receiver can decode DTS:X when it receives the information from your Blu-ray player.

DTS Neural:X

So, if you have height or upfiring speakers connected to your AV receiver, then you can enable this on stereo or standard multichannel soundtracks.

Neural:X will then create extra pseudo channels to make full use of all the speakers in your room.

Neural:X won't be available on all AV receivers, so make sure you check this before you buy.

You might also find that some AV receivers won't allow you to use this on certain types of soundtracks. For example, in the early days, many models wouldn't allow this to be selected on Dolby soundtracks.

However, that has changed recently. Still, it's something you should check if you think you might be using it.

DTS Virtual:X

Unlike DTS:X, this is not a soundtrack type that can be found on your Blu-ray disc. It’s a digital processing mode which can be used on a few different types of audio.

Not all AV receivers will support it. So, check before you buy if it’s something you want.

The aim of DTS Virtual:X is to give you the 3D experience of an object-based soundtrack – but without you having to install any height speakers. So, this can be great if you haven’t got the space – or money – for the extra hardware.

Therefore, DTS Virtual:X will work on any speaker configuration that doesn’t have any height speakers. So, 2.1, 3.1, 5.1 – even a simple soundbar setup.

You should be able to select this format on your receiver for any type of DTS soundtrack – or any PCM or multichannel PCM signal. Stereo or surround.

The only thing to be aware of is that you won’t be able to use it if you are playing any Dolby-encoded material. Dolby prevents this in their licensing agreement.

DTS Virtual:X won’t sound as effective as having actual height speakers with a true object-based soundtrack. But it can be effective in giving an extra sense of space. It can also help to make dialogue clearer.

Here’s a video from DTS that shows a bit more about it:

THX listening modes

Some models of AV receiver (often the more expensive ones!), are THX certified and may offer extra THX listening modes.

THX certification means that a product meets certain standards defined by THX,
who aim to set the highest standards for home theater video and audio
equipment. This certification isn't limited to AV receivers, and we can
find THX certified products across all types of audio-visual hardware.

Whilst we should never assume that a product without THX certification
must be of poor quality, where we find this mark of approval we should
be confident of a high-quality product.

A THX certified receiver will have THX Surround Sound Modes which
use a technology called THX Advanced Speaker Array (THX ASA).

The three
listening modes - Cinema, Games and Music - are similar to Pro Logic in
that they can play back any type of source material and match it to the
speaker setup you have in your room.

The difference with the THX listening modes is they also add
equalisation to the audio in order to tailor the original soundtrack
mix to suit a home environment. The theory is that movie soundtracks are
mixed to sound good at high volumes in movie theaters, but will sound
different at lower volumes in normal rooms.

Therefore, these modes are
designed to alter the frequency response of the sound you hear and allow
for the differences between a real movie theater and your room.

If you have these listening modes on your equipment, you may find
that you can improve the sound in your room by activating these
settings. Give it a try and see what you think.

They can be used on
their own or alongside the various Dolby and DTS modes listed above.

Other processing types

The types of decoding/processing listed above are the most common versions that we will find on many AV receivers.

However, each manufacturer will often provide further DSP (Digital Signal Processing) listening modes for you to choose from.

These extra versions will provide other processing options to alter
the sound that you hear through your system. Such types can include
alternative 'Cinema' or 'Music' modes, Classical/Rock/Pop settings
designed to enhance certain styles of music, or allow you to do things
like playing a stereo source around all your speakers whilst keeping the
original stereo image intact.

Surround Sound Formats Summary

As you can see, the surround sound formats and listening modes that AV receivers have can seem quite complex.

However, the idea is to give you the flexibility to tweak the audio
you hear to suit your room and hardware setup. There is no way a movie
can be made to sound the same in all types of rooms and with different
speaker configurations, and so at least we have the option of adjusting
the audio slightly to suit our hardware and taste.

Fortunately, many of these options will be selected automatically by
your hardware depending on the type of audio you are playing, but it can
be useful to understand the options you have for changing the settings
because it can allow you to get an even better sound in your room.

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